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United States Patent |
6,011,987
|
Barnett
|
January 4, 2000
|
Fiducial positioning cup
Abstract
A fiducial positioning cup (86) has a hemispherical well (92) in its top
and a central bore (94) from a bottom of the hemispherical well (92) to a
base of the positioning cup (86). The fiducial cup (86) is then attached
to the skin (88) of a patient. A needle (110) is passed through the
fiducial positioning cup (86) to mark an area of the patient's skin (88)
with a tattoo (112). Fiducials (84) are secured in the fiducial
positioning cups (86). Magnetic resonance or other diagnostic images are
taken. Once the images are taken, the fiducials (84) and fiducial
positioning cups (86) are removed. The tattoo mark (112) remains. The
fiducial positioning cups (86) are reattached when a stereotactic
procedure is to be performed. The needle (110) is passed through the
fiducial cups (86) and a tip of the needle (110) is aligned with the
tattooed mark (112) on the patient's skin (88). The fiducial cup (86) is
then lowered and centered over the tattooed mark (112). A stereotactic
wand (36) is aligned with the magnetic resonance image by placing a tip
(42) of the wand (36) in the fiducial cups (86) and emitting signals. The
stereotactic system decodes the signals to identify where the tip (42) of
the wand (36) is on the magnetic resonance image.
Inventors:
|
Barnett; Gene H. (Gates Mills, OH)
|
Assignee:
|
The Cleveland Clinic Foundation (Cleveland, OH)
|
Appl. No.:
|
986863 |
Filed:
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December 8, 1997 |
Current U.S. Class: |
600/414; 600/426; 606/130 |
Intern'l Class: |
A61B 005/00 |
Field of Search: |
600/410,414,407,426
128/899
606/116,130
901/46
395/89,86,93
378/205,207
|
References Cited
U.S. Patent Documents
4344183 | Aug., 1982 | Jacobson.
| |
4826487 | May., 1989 | Winter.
| |
5024727 | Jun., 1991 | Campbell et al. | 156/663.
|
5074318 | Dec., 1991 | Campbell et al. | 128/899.
|
5193106 | Mar., 1993 | DeSena.
| |
5195526 | Mar., 1993 | Michelson.
| |
5263956 | Nov., 1993 | Nobles.
| |
5368030 | Nov., 1994 | Zinreich et al.
| |
5394457 | Feb., 1995 | Leibinger et al.
| |
5397329 | Mar., 1995 | Allen | 606/73.
|
5408409 | Apr., 1995 | Glassman et al.
| |
5469847 | Nov., 1995 | Zinreich et al.
| |
5517990 | May., 1996 | Kalfas et al. | 128/653.
|
5551429 | Sep., 1996 | Fitzpatrick et al. | 128/653.
|
5575794 | Nov., 1996 | Walus et al. | 606/116.
|
5622187 | Apr., 1997 | Carol.
| |
5695501 | Dec., 1997 | Carol et al. | 606/130.
|
5732703 | Mar., 1998 | Kalfas et al. | 128/653.
|
5769789 | Jun., 1998 | Wang et al.
| |
5792147 | Aug., 1998 | Evans et al.
| |
5807252 | Sep., 1998 | Hassfeld.
| |
5852647 | Dec., 1998 | Schick et al.
| |
5878104 | Mar., 1999 | Ploetz.
| |
Foreign Patent Documents |
WO 94/17733 | Aug., 1994 | WO.
| |
Other References
Article entitled: "Computer-Assisted Coregistration of Multislice SPECT and
MR Brain Images by Fixed External Fiducials," by Robert T. Malison et al.
Published in the Journal of Computer Assisted Tomography, vol. 17, No. 6,
1993.
|
Primary Examiner: Lateef; Marvin M.
Assistant Examiner: Shaw; Shawna J.
Attorney, Agent or Firm: Fay, Sharpe, Fagan, Minnich & McKee, LLP
Claims
Having thus described the preferred embodiment, the invention is now
claimed to be:
1. A fiducial cup for a magnetic resonance imaging system for designating a
coordinate and trajectory on a subject which includes a subject support, a
frame assembly which mounts at least two receivers in a fixed relationship
to the subject, a wand defining a tip portion and a pointing axis of the
wand, and having at least two wand emitters mounted in a spaced
relationship in a fixed relationship to the pointing axis and the tip, the
emitters selectively emitting wand signals which are received by the at
least two receivers, a wand position processor for determining a position
of the wand tip portion from the wand signals from the wand emitters which
are received by the at least two receivers, an image memory for storing
image data indicative of a three-dimensional region of the portion of the
subject which is secured to the subject support means, a selecting means
for selecting data from the three-dimensional image memory, a display for
converting the selected data from the image memory into human-readable
displays, a transform processor for transforming a position of the wand
tip and trajectory into a coordinate system of the image data stored in
the image memory, at least three fiducial markers which are imaged during
generation of the image data disposed at selected subject positions when
the three-dimensional image data was acquired such that locations of the
three fiducial markers are identifiable in the three-dimensional image
data, each of the fiducial markers being supported by a respective
fiducial cup, each fiducial cup comprising:
a fiducial receiving cup having a hemispherical well, a fiducial marker,
including an imageable material, being removably secured in the
hemispherical well, the hemispherical well of the fiducial receiving cup
and the fiducial marker having a common centroid, and the hemispherical
well being accessible and defining a concave bearing surface when the
fiducial marker is removed; and
a subject surface that is adapted to be removably affixed to a subject.
2. A fiducial cup, comprising:
a fiducial receiving surface defining a hemispherical well for removably
receiving a fiducial which includes an imageable material which is imaged
in a diagnostic imaging procedure;
a subject surface that removably engages a subject;
a central bore extending from a bottom of the hemispherical well to the
subject surface; and
a screw extending through the central bore for attachment to the subject.
3. An apparatus for correlating a physical subject with diagnostic images
of the physical subject, the apparatus comprising:
at least three fiducial cups, each fiducial cup including a subject
surface, adapted to be secured to a physical subject, and a fiducial
receiving surface;
a fiducial marker received in the fiducial receiving surface of said each
fiducial cup, said each fiducial marker being spherical and containing an
imageable material such that said each of the fiducial markers is imaged
in diagnostic images;
a pointer having a tip portion including a spherical well of a common
radius with said each fiducial marker which is selectively movable to be
touched to each of the fiducial markers; and
an electronic circuit for correlating the pointer with the diagnostic
images, the physical subject being correlated with the diagnostic images
after the pointer is touched to at least three of the fiducial markers.
4. The apparatus as set forth in claim 3 wherein the imageable material has
a physical mass which is centered on a geometric center of the respective
fiducial marker, the tip of the pointer being offset from the physical
center by a radius of the respective fiducial marker.
5. The apparatus as set forth in claim 4, wherein the pointer has a virtual
tip offset from its physical tip by the common radius, such that when said
each fiducial marker is received in the concave well of the tip, the
virtual tip and the geometric center of the fiducial coincide.
6. The apparatus as set forth in claim 4, wherein the pointer tip includes
a spherical end segment of common radius with said each fiducial marker
and defines a virtual tip in an interior of the physical tip the common
radius from a surface of the spherical segment, such that when the tip is
positioned in the fiducial surface of the fiducial cup in the absence of
one of the fiducial markers, the virtual tip coincides with the physical
center of one of the fiducial markers.
7. The apparatus as set forth in claim 3, wherein the fiducial cup includes
a central bore extending between the fiducial surface and the subject
surface.
8. A method of correlating locations on a subject with a diagnostic image,
the method comprising:
a) identifying at least three locations on a subject;
b) attaching fiducial positioning cups to the at least three locations on
the subject;
c) securing respective fiducials to each of the at least three fiducial
positioning cups, each fiducial positioning cup including a central bore
and defining a well which is shaped to receive the respective fiducials;
d) performing a diagnostic imaging procedure to generate a diagnostic
image, the fiducials being identifiable in the diagnostic image;
e) correlating locations on the subject with the diagnostic image;
f) removing the fiducials from the subject; and
g) marking the subject by passing a marker through the central bore such
that the marker contacts the subject, the mark providing a reference for
repositioning the fiducial positioning cups.
9. A method of correlating locations on a subject with a diagnostic image,
the method comprising:
a) identifying at least three locations on a subject;
b) marking the subject to identify the at least three locations at which
fiducial positioning cups are to be secured on the subject;
c) attaching the fiducial positioning cups to the at least three locations
on the subject, including:
c1) inserting a needle through a central bore of each of the fiducial
positioning cups to be secured;
c2) placing a tip of the needle on the mark on the subject; and
c3) sliding the fiducial positioning cup along the needle;
d) securing respective fiducials to each of the at least three fiducial
positioning cups, the fiducial positioning cups defining a well which is
shaped to receive the respective fiducials;
e) performing a diagnostic imaging procedure to generate a diagnostic
image, the fiducials being identifiable in the diagnostic image;
f) correlating locations on the subject with the diagnostic image; and
g) removing the fiducials from the subject.
10. A method of correlating locations on a subject with a diagnostic image
of the subject, the method comprising:
a) identifying at least three locations on a subject;
b) attaching respective subject surfaces of fiducial positioning cups to
the at least three locations on the subject;
c) securing respective spherical fiducials to respective fiducial receiving
surfaces of each of the at least three fiducial positioning cups, the
fiducial receiving surfaces defining wells which are shaped to receive the
respective spherical fiducials;
d) performing a diagnostic imaging procedure to generate a diagnostic
image, the fiducials being identifiable in the diagnostic image;
e) correlating locations on the subject with the diagnostic image,
including:
e1) selectively touching a tip of a stereotactic tool to each of the
fiducials, the tip having a common radius with each of the fiducials; and
e2) correlating physical locations of the stereotactic pointer with the
diagnostic images using an electronic circuit; and
f) removing the fiducials from the subject.
11. A method of correlating locations on a subject with a diagnostic image,
the method comprising:
a) identifying at least three locations on a subject;
b) marking the subject to identify the at least three locations at which
fiducial positioning cups are to be secured on the subject;
c) attaching respective subject surfaces of the fiducial positioning cups
to the at least three locations on the subject, including:
c1) inserting a needle through a central bore of each of the fiducial
positioning cups to be attached;
c2) placing a tip of the needle on the mark on the subject; and
c3) sliding the fiducial positioning cup along the needle;
d) securing respective fiducials to respective fiducial receiving surfaces
of each of the at least three fiducial positioning cups, the fiducial
receiving surfaces defining a hemispherical well which is shaped to
receive the respective fiducials;
e) performing a diagnostic imaging procedure to generate a diagnostic
image, the fiducials being identifiable in the diagnostic image;
f) correlating locations on the subject with the diagnostic image;
g) removing the fiducials from the subject;
h) defining a virtual point on a stereotactic tool, which virtual point is
displaced from a physical point of a stereotactic pointer by a
characteristic distance, the stereotactic pointer having a tip with a
substantially same shape as each of the fiducials, the well in each of the
fiducial positioning cups being shaped to also receive the stereotactic
pointer tip, each of the fiducials containing a material including a
characteristic point which is imaged during the imaging process and which
appears in the diagnostic image, the characteristic point being displaced
from a surface of the fiducial by a characteristic distance;
i) after performing the diagnostic imaging procedure, removing each of the
fiducials from the respective fiducial positioning cups; and
j) inserting the stereotactic pointer tip in the fiducial positioning cups,
such that the virtual tip is coincident with the position which was
occupied by the characteristic portion of the respective fiducial before
the respective fiducial was removed.
12. A fiducial cup, comprising:
a fiducial receiving cup defining an open well surrounded by a curved
bearing surface that defines a cup bearing surface centroid, the cup
bearing surface being contoured for selectively receiving a bearing
surface of a tool and registering the tool relative to the cup bearing
surface centroid;
a fiducial containing an imageable material surrounding an imageable
material centroid, the bearing surface centroid and the imageable material
centroid being coincident when the fiducial is removably mounted in the
well for imaging in a diagnostic imaging procedure; and
a subject surface that is adapted to be removably affixed to a subject.
13. The fiducial cup as set forth in claim 12, further including:
a central bore extending from a bottom of the well to the subject surface.
14. The fiducial cup as set forth in claim 12, wherein the cup bearing
surface of the fiducial receiving cup includes a spherical segment well of
a common radius with the bearing surface of the tool.
15. The fiducial cup as set forth in claim 12, further including:
an adhesive which removably secures both the subject surface to the subject
and the fiducial to the fiducial receiving cup.
16. The fiducial cup as set forth in claim 12, wherein the cup bearing
surface is hemispherical for receiving a spherical fiducial.
Description
BACKGROUND OF THE INVENTION
The present invention relates to the medical diagnostic and surgical arts.
It finds particular application in conjunction with stereotactic surgery
and will be described with particular reference thereto. However, it is to
be appreciated that the invention will also find application in
conjunction with minimally invasive surgery, neurosurgery, neurobiopsy,
CT-table needle body biopsy, breast biopsy, endoscopic procedures,
orthopedic surgery, other invasive medical procedures, industrial quality
control procedures, and the like.
Three-dimensional diagnostic image data of the brain, spinal cord, and
other body portions are produced by CT scanners, magnetic resonance
imagers, and other medical diagnostic equipment. These imaging modalities
typically provide structural detail with a resolution of one millimeter or
better. Various frameless stereotaxy procedures have been developed which
take advantage of three-dimensional image data of the patient. These
procedures include guided-needle biopsies, shunt placements, craniotomies
for lesion or tumor resection, and the like. Another area of frameless
stereotaxy procedure which requires extreme accuracy is spinal surgery
including screw fixation, fracture decompression, and spinal tumor
removal.
In brain biopsy procedures, for example, surgeons or other medical
personnel drill and tap a hole in a patient's skull. Surgeons have come to
rely on frameless stereotaxy procedures for placing and orienting the bit
of the surgical drill prior to forming the hole in the skull. These
procedures require aligning images of fiducials or markers, affixed at
three or more spaced points on the patient's body, with known fiducial
positions in patient space. The fiducials are spherical markers or small
beads that are injected with radiation opaque and magnetic resonance
excitable materials and fit within a fiducial positioning cup. Therefore,
the fiducials are visible in the imaging medium selected such that they
show up as readily identifiable dots in the resultant image data.
Heretofore, the fiducials have been affixed directly to the patient's body
using a glue. Fiducials have also been attached to a patient's skull using
screws. However, these methods of attachment have proven undesirable,
especially if it is necessary to remove,the fiducials for a period of time
before they are reattached. Because the imaging modalities discussed above
typically provide structural detail with a resolution of a millimeter or
better, it is critical that the fiducials be reattached as close as
possible to the exact location where they were previously located. Such
accuracy is difficult to achieve when using a glue to attach the small,
spherical fiducials directly to the patient's body.
The present invention provides a new and improved apparatus and method
which overcomes the above-referenced problems and others.
SUMMARY OF THE INVENTION
A fiducial cup for a magnetic resonance imaging system for designating a
coordinate and trajectory on a subject includes a subject support. A frame
assembly mounts at least two receivers in a fixed relationship to the
subject. A wand defines a tip portion and a pointing axis of the wand. At
least two wand emitters are mounted in a spaced relationship in a fixed
relationship to the pointing axis and the tip. The emitters selectively
emit wand signals which are received by the at least two receivers. A wand
position processor determines a position of the wand tip portion from the
wand signals from the wand emitters which are received by the at least two
receivers. An image memory stores image data indicative of a
three-dimensional region of the portion of the subject which is secured to
the subject support means. A selecting means selects data from the
three-dimensional image memory. A display converts the selected data from
the image memory into human-readable displays. A transform processor
transforms a position of the wand tip and trajectory into a coordinate
system of the image data stored in the image memory. At least three
fiducials are imaged during generation of the image data. The fiducials
are disposed at selected subject positions when the three-dimensional
image data is acquired such that locations of the three fiducials are
identifiable in the three-dimensional image data. The fiducials are
supported by fiducial cups. Each fiducial cup comprises a fiducial
receiving surface against which the fiducial is removably mounted. A
subject surface is removably affixed to the subject.
In accordance with one aspect of the invention, the fiducial receiving
surface includes a hemispherical well.
In accordance with a more limited aspect of the invention, a central bore
extends from a bottom of the hemispherical well to the subject surface.
In accordance with another aspect of the invention, the fiducial receiving
surface has a spherical segment well of a common radius with the wand tip
for rotatably receiving the wand tip therein.
In accordance with another aspect of the invention, an adhesive secures the
subject surface to the subject and a fiducial to the fiducial surface.
In accordance with a more limited aspect of the invention, a screw extends
through the central bore for attachment to the subject.
One advantage of the present invention is that it improves the accuracy of
positioning and repositioning of fiducials.
Another advantage of the present invention is that it improves the accuracy
with which the diagnostic images are aligned with the patient.
Another advantage of the present invention is that the fiducials are
securely held within the fiducial positioning cups.
Another advantage of the present invention is that the fiducial positioning
cups include a larger surface area, relative to the fiducials, for
contacting to the patient's skin.
Still further advantages of the present invention will become apparent to
those of ordinary skill in the art upon reading and understanding the
following detailed description of the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may take form in various components and arrangements of
components, and in various steps and arrangements of steps. The drawings
are only for purposes of illustrating a preferred embodiment and are not
to be construed as limiting the invention.
FIG. 1 is a perspective view of an operating room in which the present
invention is deployed;
FIG. 2 is a block diagram of the image data manipulation of the present
system of FIG. 1;
FIG. 3 illustrates the wand;
FIG. 4 is illustrative of a preferred coordinate transform between the
coordinate system of the data and the patient;
FIG. 5 illustrates a fiducial positioning cup on the surface of a patients
skin;
FIG. 6 illustrates the steps of positioning and repositioning a fiducial
positioning cup and a fiducial;
FIG. 7 illustrates a needle inserted through the fiducial cup for tattooing
a mark in the patient's skin;
FIG. 8 illustrates a fiducial positioning cup having a tattooed mark below
the bore;
FIG. 9 illustrates the fiducial inserted into the fiducial positioning cup;
FIG. 10 illustrates the needle aligned with the tattooed mark for
repositioning the fiducial cup;
FIG. 11 illustrates the repositioned fiducial cup held in place by
adhesive;
FIG. 12 illustrates the fiducial cup held in place by a screw;
FIG. 13 illustrates a convex hemispherical wand tip placed in the fiducial
cup; and
FIG. 14 illustrates a concave hemispherical wand tip placed on a spherical
fiducial held in the fiducial cup.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIG. 1, a subject, such as a human patient is received on
an operating table or other subject support 10 and appropriately
positioned within the operating room. A frame 12 is mounted in a fixed
relationship to the patient such that it is precisely positioned within
the subject or subject support coordinate system. In the illustrated
embodiment, the frame 12 is mounted to the patient support 10. Mounting
the frame 12 to the patient support 10 permits the support to be turned,
raised, lowered, wheeled to another location, or the like, without
altering the patient coordinate system. Alternatively, the support may be
mounted to a pole or other stationary support, the ceiling of the room, or
the like. The frame 12 supports a plurality of receivers 14 such as
microphones, radio frequency receivers, light sensitive diodes, other
light sensitive receivers, and the like mounted at fixed, known locations
thereon. A securing means, such as a head clamp 16, securely positions a
portion of the subject into the frame of reference of the frame 12.
With continuing reference to FIG. 1 and further reference to FIG. 2, an
operator console 18 houses a computer system 22 and a data memory 24. The
stored three-dimensional image data preferably contains a video pixel
value for each voxel or point in a three-dimensional rectangular grid of
points, e.g. a 256.times.256.times.256 grid. Selectable orthogonal and
other oblique planes of the data can readily be withdrawn for display from
the three-dimensional memory 24 by a plane or slice selector 26 using
conventional technology.
For example, the pixel values which lie on a selected axial, sagittal,
coronal, and oblique planes are copied into corresponding image memories
28a, 28b, 28c, 28d. A video processor 32 converts the two-dimensional
digital image representations from one or more of the image memories 28
into appropriate signals for display on video monitors 34 or other
appropriate image displays.
With continuing reference to FIG. 1 and further reference to FIG. 3, a wand
36, formed of suitable material such as metal, has a hemispherical tip
portion at a proximal end 42. The tip is connected to a portion extending
along a pointing axis 44 of the wand. In the illustrated embodiment, a
first emitter 46 is located at (x.sub.1, y.sub.1, z.sub.1) along the axis
44 a fixed known distance l.sub.1 from the tip 42. The second emitter 48
is at (x.sub.1 +.DELTA.x.sub.2, y.sub.1 +.DELTA.y.sub.2, z.sub.1
+.DELTA.z.sub.2), where .DELTA.x.sub.2, .DELTA.y.sub.2 and .DELTA.z.sub.2
represent constant values based on the geometry of the second emitter 48
relative to the tip 42. The third emitter 52 is at (x.sub.1
+.DELTA.x.sub.3, y.sub.1 +.DELTA.y.sub.3, z.sub.1 +.DELTA.z.sub.3), where
.DELTA.x.sub.3, .DELTA.y.sub.3 and .DELTA.z.sub.3 represent constant
values based on the geometry of the third emitter 52 relative to the tip
42.
Emitters 46, 48, 52 emit infra-red positioning signals used by a locator
system 54 to locate a coordinate and trajectory of the wand. Infra-red
signals are received from each of the emitters at the two receivers. The
three infrared signals received by each receiver are used to calculate the
axis 44 and the location of the tip. The plane or slice selector 26 (FIG.
2) selects patient image planes based on the coordinate and trajectory
located. It is to be appreciated that more than three emitters, may be
mounted on the wand to provide additional positioning signals to be used
by a locator system to locate the coordinate and trajectory of the wand.
Furthermore, it is to be Understood that the emitters 46, 48, 52 may also
emit spark or radio frequency signals which are received by the receivers
14.
With reference to FIG. 4, before the wand 36 can be used to locate a proper
coordinate and trajectory for a surgical tool such as a drill, the patient
;pace or coordinate system (x, y, z) is aligned with the image space or
coordinate system (x', y', z') stored in memory. Aligning the spaces
begins with referencing known positions or points 78 in the patient space
with the wand tip 42. For example, the tip of the wand may be referenced
to three fiducials, tattoo marks, or characteristic physical anatomy, e.g.
the tips of the spinous and traverse processes. These known points 78 are
compared with corresponding position of pixels 82 in the image space.
With reference to FIGS. 5 and 6, a positioning cup 86 is placed on the
surface of the patient's skin 88 in a step A. Each positioning cup 86 is a
base into which one of the fiducials 84 is attached. Furthermore, the cups
86 each have a hemispherical (or slightly less than a half sphere) well 92
in its top and a central bore 94 from the bottom of the hemisphere 92 to a
base 96 of the cup. The fiducial positioning cup 86 is preferably
invisible to the imaging medium selected such that it does not show up in
the resultant image data. Preferably, the positioning cup 86 is glued to
the patient's skin 88.
As described above, image data, including the fiducials affixed at the
three or more spaced points on the patient's body, is aligned with the
patient space containing physical fiducials 84. Therefore, the fiducials
84 and the positioning cups 86 ideally remain fixed in place during the
time interval between which the image data is gathered and the stereotaxy
procedure is performed. However, because this time interval may be several
hours, or even days, the cups are not always kept in place. Rather, they
are removed and reattached later.
To facilitate accurately repositioning the cups 86, FIGS. 6 and 7
illustrate that in a step B, before the fiducials 84 are attached in the
cup or after the fiducials are removed from the cup, a tattoo needle 110
is inserted through the bore 94 to place a small tattoo mark 112 (see FIG.
8) on the patient's skin 88. Thereafter, in a step C the fiducial 84 is
affixed to the support (see FIGS. 6 and 9), preferably using adhesive, and
the image data is gathered. After the image data is obtained, the
positioning cups 86 are removed in a step D of FIG. 6. The tattoo marks
112, however, remain visible.
Before the stereotaxy procedure is performed, the three cups 86 are
re-affixed to the patient's skin 88 in a step E of FIG. 6. With reference
to FIG. 10, the needle 110 is inserted through the central bore 94 of a
fiducial positioning cup 86 to be secured. The tip of the needle 110 is
then placed on the mark 112 on the subject. The fiducial positioning cup
86 is then slid along the needle 110 until it contacts the patients skin
88. Because the tip of the needle 110 is located in the tattooed spot 112,
the support 86 is accurately positioned so that it is centered on the
tattooed spot 112. Preferably, as illustrated in FIG. 11, the fiducial
positioning cups 86 are then secured to the subject. Alternatively, as
illustrated in FIG. 12, a surgical screw 114 is inserted into the
respective bore to affix' the fiducial support 86 to the patient's skull
or other boney plate.
As already discussed above in reference to FIG. 4, the positions of the
three fiducials 84 are compared with the relative position of the images
82 of the centroids of the fiducials in the image space. Actuating the
emitters while the tip of the wand is touching each of its characteristic
patient space points (x, y, z) defines these points electronically. Like
coordinates (x', y', z') of the image pixels 82 are defined electronically
from the electronic image and compared to the patient space coordinates
(x, y, z). As illustrated in FIG. 13, the wand 36 preferably has a convex
hemispherical end which is inserted into each of the respective fiducial
supports 86. After the emitters are actuated, a virtual tip 116 of the
wand is then correlated with a centroid of the fiducial in the electronic
image. The virtual tip is defined at the geometric center of the sphere
defined by the hemispherical tip. Because the hemispherical tip 42 of the
wand is the same radius as the fiducial 84, the virtual tip 116 of the
wand is located at the centroid of the fiducial, regardless of the wand's
trajectory.
As illustrated in FIG. 14, in an alternative embodiment, the wand 36 has a
concave partial spherical in its tip 42 which contacts the spherical
surface of the fiducial 84. In this embodiment, the virtual tip 116' of
the wand is calculated to be the geometric center of the partial spherical
surface which falls at the centroid of the fiducial when the tip is
against the fiducial. In either of the two embodiments, the virtual tip of
the wand is offset from the physical tip.
Having aligned the image and patient spaces, a wand with its physical and
virtual tips aligned can be used to identify the entry coordinate and
trajectory at which the surgical tool will be applied to the patient. The
surgeon maneuvers the wand to a proposed trajectory and actuates the
emitters. Signals from the emitters are used to calculate the trajectory
and the end point of the wand. The trajectory and end point are displayed
on the monitor superimposed on the three-dimensional image or selected
image plane(s).
By viewing the display, the surgeon identifies the location of the wand tip
with respect to anatomic structure, and the trajectory of the bore. If the
trajectory is unsatisfactory, the wand is repositioned and its new
trajectory determined and evaluated.
The invention has been described with reference to the preferred
embodiment. Obviously, modifications and alterations will occur to others
upon reading and understanding the preceding detailed description. It is
intended that the invention be construed as including all such
modifications and alterations insofar as they come within the scope of the
appended claims or the equivalents thereof.
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